The present invention relates to a mold having a moving joint face for making a plastics material piece, and to a method using such a mold.
It is known to make pieces out of plastics material by injection molding or by extrusion-compression methods in a two-part mold defining a recess.
Each of the two parts of the mold has a peripheral zone for coming into contact with the peripheral zone of the other part of the mold.
The joint face of the mold is the face defined by these two peripheral zones when they bear against each other.
In some cases, the peripheral zones of the mold parts cannot be plane. However even under such circumstances, the term joint xe2x80x9cfacexe2x80x9d is still used to designate the surface constituted by the two peripheral zones that bear one against the other.
It is also known to make pieces out of reinforced plastics material comprising one or more reinforcing sheets that can be constituted, for example, by mats of reinforcing fibers or by fabrics; e.g. those known under the initials HTPC.
This reinforcing sheet is placed in the open mold, e.g. on the punch, i.e. the male portion of the mold, and then the mold is closed. A certain quantity of plastics material is then delivered to the mold either by extrusion before it is closed or by injection after it is closed.
Those known methods of making reinforced plastics material pieces give satisfaction, but they require a certain amount of retouching work since the reinforcing sheet does not always take up exactly the proper location in the mold, such that some of its peripheral edges are sometimes pinched in the joint face of the mold between the two pressed-together peripheral zones of the two mold parts.
A trimming operation is then necessary on leaving the mold in order to remove those portions of the reinforcing sheet that project outside the part.
The present invention seeks to provide a mold whose structure prevents the risk of a sheet becoming pinched in its joint face.
The present invention provides a mold for making a plastics material piece, the mold comprising two parts defining between them a cavity corresponding to the piece that is to be made, each mold part having a peripheral zone for coming into contact with the peripheral zone of the other mold part, the two zones, when united, defining the joint face of the mold, wherein one of the mold parts is designed to receive a sheet and is made up of two blocks, namely a central block defining substantially the mold cavity and a peripheral block supporting the peripheral zone, the two blocks being suitable for sliding relative to each other in the mold closure direction, the peripheral block being movable so as to move the peripheral zone of said peripheral block away from the edges of the sheet.
The mold of the invention presents the advantage that the peripheral block can be moved prior to the operation of closing the mold in such a manner that a sheet already inserted in the mold cannot be pinched in the joint face of the mold when the mold closes.
With the mold of the invention it is possible to begin by placing the reinforcing sheet (or any other sheet for incorporation or overmolding in the piece that is to be made) in the two-block part of the mold.
With the mold being held open, the peripheral block is then moved in such a manner as to cause its peripheral zone to move away from the sheet, so as to be sure that the peripheral edges of said sheet do not project over the peripheral zone defining the joint face.
Once the peripheral block has been moved, the other mold part is moved into position until its peripheral zone comes to bear on the peripheral zone remote from the sheet.
At this stage, the joint face of the mold has been reconstituted by the two peripheral zones of the two mold parts bearing against each other at a distance from the sheet that is sufficient to guarantee that it is not pinched in the joint face.
Finally, the peripheral block is moved back into the molding position while keeping the two peripheral zones in contact, thereby finally closing the mold which is thus returned to its normal molding configuration.
The plastics material can be introduced by injection at the end of the above-described operations, or by extrusion at a moment when the mold is still open.
The peripheral block may also have actuators controlling holding rods.
The invention also provides a method of using a mold as specified above and comprising the following steps:
placing a sheet for incorporation or overmolding in the piece that is to be made in the two-block part of the mold;
moving the peripheral block so as to move the peripheral zone away from the edges of the sheet;
closing the mold by bringing the peripheral zone of the other mold part into contact with the peripheral zone of the peripheral block; and
returning the peripheral block to the molding position while keeping the two peripheral zones in contact.
The peripheral block is preferably moved without displacing or touching the sheet.
The invention also provides a method of using a mold to make a plastics material piece, the mold comprising two parts defining between a cavity corresponding to the piece to be made, each mold part having a peripheral zone for coming into contact with the peripheral zone of the other mold part, the two zones, when united in this way, defining the joint face of the mold, one of the mold parts being made up of two blocks, namely a central block substantially defining the mold cavity and a peripheral block both supporting the peripheral zone and having actuators which control holding rods, the two blocks being suitable for sliding relative to each other in the mold closure direction, said method comprising the following steps:
placing a reinforcing sheet for incorporation or overmolding in the piece to be made in the two-block part of the mold;
moving the peripheral block to move the peripheral zone away from the edges of the reinforcing sheet;
actuating the actuators to bring the holding rods against the reinforcing sheet;
retracting the actuators;
closing the mold by bringing the peripheral zone of the other mold part into contact with the peripheral zone of the peripheral block; and
returning the peripheral block to the molding position while keeping the two peripheral zones in contact.
The reinforcing sheet can optionally be preformed outside the mold.
The peripheral block can optionally be moved upwardly to move the peripheral zone away from the edges of the reinforcing sheet.